plugin XEP-0353: fix jingle initiation on disco "Service Unavailable" error:

When requesting disco info on a bare jid which is not in our roster, server may return
"Service Unavailable" (to avoid leaking valid JIDs). In this case, the initiation was
failing, this is now fixed by using empty categories in this case.

sat/plugins/plugin_xep_0353.py

@@ -19,7 +19,7 @@
 from zope.interface import implementer
 from twisted.internet import defer
 from twisted.internet import reactor
-from twisted.words.protocols.jabber import xmlstream, jid
+from twisted.words.protocols.jabber import xmlstream, jid, error
 from twisted.words.xish import domish
 from wokkel import disco, iwokkel
 from sat.core.i18n import _, D_
@@ -85,8 +85,15 @@ class XEP_0353:
         if peer_jid.resource:
             return True
 
-        infos = await self.host.memory.disco.getInfos(client, peer_jid)
-        categories = {c for c, __ in infos.identities}
+        try:
+            infos = await self.host.memory.disco.getInfos(client, peer_jid)
+        except error.StanzaError as e:
+            if e.condition == "service-unavailable":
+                categories = {}
+            else:
+                raise e
+        else:
+            categories = {c for c, __ in infos.identities}
         if "component" in categories:
             # we don't use message initiation with components
             return True